The present invention relates to electrical power supplies, and particularly to electrical power supplies which are essentially (but not exclusively) useful for certain medical devices, such as respirators, which may be connected either to an AC source or a DC source.
Power supplies for medical applications, such as respirators, require a very high degree of electrical safety. Such power supplies must frequently be capable of operating from an AC source such as AC household current, as well as from a DC source such as a standby battery or an automotive vehicle battery. Generally, the two power sources are isolated from each other, and/or special precautionary controls are provided, to prevent malfunction or exposing the user to a dangerous voltage if the two sources are plugged in at the same time. In addition, users are also generally required to preset the electrical device for an AC source or a DC source before turning-on the device. Failure to properly preset the electrical device, which can easily occur, may result in damage to the electrical appliance and/or a hazardous condition to the user.